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During hot forging/forming operations, the die surface and near surface region is subjected to severe wear. The failure of dies originates from the surface region. In this research work, plasma nitriding was done on two hot forming tool steels namely AISI H11 and AISI H13. The aim is to develop a hard and wear resistance surface required for hot forming operations. The mechanical and microstructural properties of the developed nitrided layer were critically examined. Thereafter the tribological characteristics of the untreated and plasma-nitrided specimens were studied on high-temperature pin-on-disc tribometer under the constant load of 25 N, sliding speed 0.5 m s −1 , sliding distance of 1500 m at different temperatures ranging from room temperature to 600°C. The results showed that the main wear mechanisms is predominantly adhesive at room temperatures and 200°C and a combination of adhesive and abrasive at elevated temperatures (400°C and 600°C).

Slurry erosion performance of detonation gun (D-gun) spray ceramic coatings (Al 2 O 3 and Al 2 O 3 -13TiO 2 ) on CF8M steel has been investigated. Slurry collected from an actual hydro power plant was used as the abrasive media in a high speed erosion test rig. Attempt has been made to study the effect of concentration (ppm), average particle size and rotational speed on the slurry erosion behaviour of these ceramic-coated steels under different experimental conditions. The analysis of eroded samples was done using SEM, XRD and stylus profilometry. The slurry erosion performance of the D-gun spray Al 2 O 3 -13TiO 2 -coated steel has been found to be superior to that of Al 2 O 3 -coated steel. Both the coatings showed brittle fracture mechanism of material removal during the slurry erosion exposure.

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Degradation of the hydroturbine components due to slurry erosion is a serious issue, especially for the hydropower plants situated on the rivers originating from Himalayas in India. In the current investigation, slurry erosion performance of two stainless steels (CA6NM and CF8M), which are commonly used in hydroturbine power plants, has been studied. A high-speed erosion test apparatus was used for the studies. Slurry collected from an actual hydropower plant was used as the abrasive media in the test apparatus. The effect of slurry concentration (ppm), average particle size of slurry particles and rotational speed on the slurry erosion behaviour was investigated under different experimental conditions. The analysis of eroded samples was done using scanning electron microscopy (SEM) and stylus profilometry. SEM images showed signatures of formation of lips, ploughing, crater and microcutting on eroded surface of steels.

Various aspects such as development, experimentation, and analysis have been covered in the present work to examine the behavior of test coatings under slurry erosion. The primary objective of the present study was to establish the specific mass loss from the test coatings under various slurry environmental conditions and highlights the importance of the addition of alumina in improving the slurry erosion resistance of Ni-TiO 2 coating. To attain this objective, two powder compositions, viz. Ni-20TiO 2 and Ni-15TiO 2-5Al 2 O 3 were deposited onto the CA6NM grade hydro-turbine steel using high velocity frame spray process. The microstructural characterization of the coatings was done by employing surface roughness tester, scanning electron microscope/energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques, whereas mechanical analysis was carried out using micro-hardness and bond strength tester. The slurry erosion tests were performed using an indigenously fabricated high speed slurry erosion test rig at different levels of rotational speed, average particle size of erodent, and slurry concentration in order to explore their effects on slurry erosion performance of test coatings. The slurry erosion results, as well as scanning electron microscope observations of eroded specimens, revealed higher slurry erosion resistance of Ni-15TiO 2-5Al 2 O 3 coating in comparison with Ni-20TiO 2 coating. Furthermore, each operational parameter was found to have a proportional effect on specific mass loss in case of both the coatings.

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